Only update LastPolled on successful poll, reset cellular chart state on mount/unmount

Failed polls no longer stamp LastPolled, so the timer retries on the
next tick instead of waiting the full polling interval. Previously SSH
failures during modem reboots created extended data gaps.

Cellular chart module now resets all state (time range, filters, custom
range) in both mount and unmount, matching the SFP chart pattern. Fixes
stale 1h view persisting when navigating back from the dashboard.

Author: tvancott42

src/NetworkOptimizer.Web/Services/CellularModemService.cs

@@ -218,8 +218,7 @@ private ModemPollContext ToPollContext(ModemConfiguration modem)
 
             if (stats != null)
             {
-                // Update LastPolled in database
-                await UpdateModemConfigAsync(modem.Id, null);
+                await UpdateModemConfigAsync(modem.Id, null, success: true);
 
                 lock (_lock)
                 {
@@ -234,14 +233,14 @@ private ModemPollContext ToPollContext(ModemConfiguration modem)
             }
             else
             {
-                await UpdateModemConfigAsync(modem.Id, "Poll returned no data");
+                await UpdateModemConfigAsync(modem.Id, "Poll returned no data", success: false);
                 return (false, "Failed to poll modem - no data returned");
             }
         }
         catch (Exception ex)
         {
             _logger.LogError(ex, "Error refreshing modem {Name}", modem.Name);
-            await UpdateModemConfigAsync(modem.Id, ex.Message);
+            await UpdateModemConfigAsync(modem.Id, ex.Message, success: false);
             return (false, $"Error: {ex.Message}");
         }
     }
@@ -336,7 +335,7 @@ private async Task PollAllModemsAsync()
         }
     }
 
-    private async Task UpdateModemConfigAsync(int modemId, string? error)
+    private async Task UpdateModemConfigAsync(int modemId, string? error, bool success)
     {
         try
         {
@@ -346,7 +345,8 @@ private async Task UpdateModemConfigAsync(int modemId, string? error)
             var config = await repository.GetModemConfigurationAsync(modemId);
             if (config != null)
             {
-                config.LastPolled = DateTime.UtcNow;
+                if (success)
+                    config.LastPolled = DateTime.UtcNow;
                 config.LastError = error;
                 config.UpdatedAt = DateTime.UtcNow;
                 await repository.SaveModemConfigurationAsync(config);

src/NetworkOptimizer.Web/wwwroot/js/cellular-charts.js

@@ -282,6 +282,15 @@ function shiftWindow(container, direction) {
 }
 
 export async function mount(elId) {
+    // Reset all state in case unmount didn't complete (Blazor Dispose race)
+    stopPoll();
+    currentRangeHours = 24;
+    windowOffset = 0;
+    isCustomRange = false;
+    customFrom = null;
+    customTo = null;
+    modemMeta = [];
+    visibility = {};
     containerId = elId;
     const container = document.getElementById(elId);
     if (!container) return;
@@ -393,10 +402,18 @@ export function soloModem(modemId) {
 export function unmount() {
     stopPoll();
     if (visibilityObserver) { visibilityObserver.disconnect(); visibilityObserver = null; }
+    if (fetchController) { fetchController.abort(); fetchController = null; }
     if (rsrpChart) { rsrpChart.destroy(); rsrpChart = null; }
     if (rsrqChart) { rsrqChart.destroy(); rsrqChart = null; }
     if (snrChart) { snrChart.destroy(); snrChart = null; }
     if (qualityChart) { qualityChart.destroy(); qualityChart = null; }
+    containerId = null;
     modemMeta = [];
     visibility = {};
+    currentRangeHours = 24;
+    windowOffset = 0;
+    isCustomRange = false;
+    customFrom = null;
+    customTo = null;
+    isInViewport = true;
 }